The present invention relates to modems for transmitting and receiving data over a transmission channel and, more particularly, to a simple and inexpensive modem which will make feasible the low cost transmission of such data.
As opposed to twisted pair or wireless transmission channels, a coaxial transmission channel offers greater noise immunity, greater enhanced capacity, self-powering capability, stability, single entity distribution, and the possibility of coexistent multi-purpose modulation schemes. Coaxial transmission channel allocations are not subject to governmental regulations as are wireless transmission channels and they require less circuit complexity and result in improved security from interference in eavesdropping. To achieve these advantages of coaxial transmission channels, however, it is necessary to preserve cable environmental integrity, reliability and data transmission transparency from interference.
As the data processing and transmission industry seeks a universal transmission medium, there must be considered such diverse criteria as topology, reliability, integrity, security, safety, flexibility, standards, environment, functionality, redundancy, and, perhaps the most important, cost. Recent integration of RF circuitry which allow both adequate performance and cost effectiveness have provided the building blocks which can be used to make reliable, low cost, universal modems.
Thus, the modem according to the present invention is comprised of only three active integrated circuits - the transmitter, the receiver, and the switch/interface network. This modem acts as a half-duplex transparent medium between peripheral devices over the coaxial transmission line. The data is preserved as an envelope on the RF waveform without the conditioning of Manchester, diphase or any additional error correcting codes.